A new radiographic method for detection of tibial component migration in total knee arthroplasty.

In a prospective study the accuracy of a new radiographic method, Matched Indicators for Radiographic Assessment (MIRA), used to assess tibial component migration in total knee arthroplasty was evaluated. Radiopaque markers were placed in the tibial component and the tibial metaphysis in a standardized way so that four vertical distances could be measured on standard radiographs. Subsidence during the first postoperative year was measured both with this new method and with roentgen stereophotogrammetric analysis in 27 Freeman-Samuelson total knee arthroplasties. The error of measurement of MIRA was determined using the known error of roentgen stereophotogrammetric analysis. The new method was found to be promising with an accuracy of 1 mm, and the correlation between MIRA and roentgen stereophotogrammetric analysis was high when subsidence exceeded this value. Therefore, subsidence of clinical importance should be detected with MIRA. The method is simple and well suited for routine follow-up examination of large patient materials.